This patent disclosure covers the internal structures and processing of self-healing materials, including metal matrix composites, which exhibit self-healing behavior. The most popular types of self-healing materials are those that are designed to mimic human skin and bones, which can heal itself as needed. When these “self-healing” materials are cracked or damaged, a healing agent can be triggered to flow into the damaged area to “heal” the damage, much like a cut in human skin triggers blood flow to promote healing. Another concept in self-healing is where the cracks in materials are subjected to compressive stresses to close them or to have material diffuse into the cracks or voids to close them. As engineering systems are becoming more sophisticated they need to take on more of the characteristics of biological systems. There is an obvious potential benefit in copying biological reliability strategies in materials manufactured and used in industry. While the basic concepts of this invention are demonstrated mainly by metallic materials, they are applicable to all type of materials, including polymers, ceramics and cementitions materials.
The composite disclosed in this work consists of an alloy matrix with hollow macro, micro and nanotubes or balloons or fibers as reinforcements, which encapsulate a lower melting point alloy (the healing agent). In this invention, the self-healing concept will be deemed successful as a result of the flow of the “healing agent” into the crack, which will lead to the recovery of a percentage of the original mechanical properties in metallic matrices. Another type of self-healing material described in this work is where the cracks are subjected to compressive stresses due to phase transformations, including those in nano structure of matrix materials and reinforcements which may be nanosize themselves.
One of the concepts of self-healing involves the flow of the healing agent into the crack, which will then be sealed through solidification of the healing agent with or without reactions with alloy matrices. The matrix will then have recovered a percentage of its original uncracked mechanical properties. The liquidus temperature of the low melting material which heals the cracks is defined as the healing temperature. When the alloy reaches the healing temperature it will be completely molten, and due to the internally or externally generated pressure or capillary pressure and surface tension, it will flow out of the ceramic tube and into the crack. When the temperature decreases or a reaction occurs with the matrix, the alloy will be solidified and will seal the crack.
The composite disclosed in this invention also includes self healing metal matrices including nanostructured matrix materials in which ultra fine or nanosize reinforcements of shape memory alloys or other reinforcements which can help compressively shut or help heal cracks, or seal a void by enhancing diffusion, are incorporated to impart self-healing characteristics.